(a) Technical Field
The present invention relates to a battery cell, and more particularly, to a pouch type battery cell capable of blocking a flow of current at the time of generation of overcharge.
(b) Description of the Related Art
In accordance with an increase in the use of portable electrical products such as video cameras, cell phones, personal computers (PCs), tablets, and the like, the importance of a secondary battery for use with such products as a driving power supply has increased.
The secondary battery that may be charged and discharged has been actively studied in accordance with the development of state-of-the-art fields such as a digital camera, a cellular phone, a laptop computer, a power tool, an electric bicycle, an electric vehicle, a hybrid vehicle, a large-capacity power storage, and the like.
Particularly, a lithium secondary battery has energy density per unit weight higher than that of other secondary batteries such as an existing lead storage battery, nickel-cadmium battery, nickel-hydrogen battery, nickel-zinc battery, and the like, and may be rapidly charged. Therefore, the use of a lithium secondary battery has increased.
The lithium secondary battery, which has an operating voltage of 3.6V or more, is used as a power supply of a portable electronic device, or a plurality of lithium secondary batteries connected to each other in series or in parallel are used in a high output electric vehicle, hybrid vehicle, power tool, electric bicycle, power storage, uninterruptible power supply (UPS), and the like.
Since the lithium secondary battery has an operating voltage three times higher than that of a nickel-cadmium battery or a nickel-metal hydride battery and has energy density characteristics per unit weight better than those of the nickel-cadmium battery or the nickel-metal hydride battery, the use of the lithium secondary battery has rapidly increased.
A lithium ion battery using a liquid electrolyte typically is used in a form in which it is welded and sealed using a metal can having a cylindrical shape or a prismatic shape as a container. A can type secondary battery using the metal can as the container has a fixed form, which limits a design of an electrical product using the can type secondary battery as a power supply and makes it difficult to reduce the volume thereof. Therefore, a pouch type secondary battery in which an electrode assembly and an electrolyte are put and sealed in a pouch package formed of a film has been developed and used.
However, in the case in which the lithium secondary battery is overheated, there is a risk that the lithium secondary battery will explode, such that it is important that the lithium secondary battery be packaged in a stable manner, so as to avoid explosion.
Overheating of the lithium secondary battery is generated due to several causes. One of these causes may be a case in which an over-current of a limit or more flows through the lithium secondary battery. When the over-current flows, heat is generated in the lithium secondary battery by Joule's heat, such that an internal temperature of the lithium secondary battery rapidly rises. In addition, the rapid rise in the internal temperature causes a decomposition reaction of an electrolyte solution to generate thermal runaway, which can lead to the explosion of the lithium secondary battery. The over-current is generated in the case in which a sharp metal object penetrates through the lithium secondary battery, insulation between a cathode and an anode is broken due to shrinkage of a separator interposed between the cathode and the anode, or a rush current is applied to the lithium secondary battery due to abnormality of a charging circuit or a load connected to the outside.
Therefore, the lithium secondary battery is used in a state in which it is coupled to a protection circuit in order to be protected from an abnormal situation such as a situation in which the over-current is generated, and a fuse element irreversibly disconnecting a line through which a charging or discharging current flows when the over-current is generated is generally included in the protection circuit. However, in the case in which the fuse element malfunctions, internal pressure of the lithium secondary battery configuring a battery module and/or a battery pack, that is, a battery cell, may be continuously increased, such that there is a risk such as ignition, explosion, or the like.
Therefore, there is a need to more securely block a flow of a current at the time of an increase in the internal pressure of the battery cell to secure safety.